1. Field of the Invention
The present invention relates to a constant velocity joint of the double Cardan type, and more particularly to a constant velocity joint suitable for use in the steering system of a vehicle such as an automobile, wherein the break angle between the input and output rotary shafts of the joint is often relatively widely changed according to the option of the user.
2. Description of the Prior Art
As a constant velocity joint of the double Cardan type for connecting two rotary shafts in a torque transmitting relation with an angle of intersection, or break angle, between the central axes thereof, there is shown in Japanese Patent Publication 50-21610 a joint construction which comprises a pair of flange yokes each having an annular flange portion and a pair of arm portions and assembled together so that the annular flange portions flatly join one another with each pair of arm portions extending away from one another, a pair of pin yokes each having a connection end portion, a spherical end portion and a pair of arm portions connecting the connection end portion and the spherical end portion, a pair of cross pieces each pivotably connecting the arm portions of each one of the flange yokes and the arm portions of each one of the pin yokes in a manner of universal joint, a centering disk having a substantially circular disk body and a transverse socket portion provided at a diametrical center of the disk body for receiving the spherical end portions of the pair of pin yokes, and a pair of thin annular disks disposed at opposite sides of the centering disk so that outer peripheral portions of the centering disk is engaged in a radially inwardly open annular groove defined by the flange portions of the pair of flange yokes via the pair of thin annular disks to be in a sliding engagement with the inside wall surfaces of the annular groove.
In such a constant velocity joint, the spherical end portions of the pair of pin yokes are maintained in a transverse alignment by the socket portions of the centering disk, so that the joint operates at a higher velocity constancy than a double Cardan joint having no such centering disk. The pair of thin annular disks seal the inside space of the annular groove off from the environment, thereby preventing foreign materials such as dusts from entering into the annular groove.
However, in such a known constant velocity joint, since the socket portion is provided at the diametrical center of the body of the centering disk, the center disk can freely rotate around the central axis of the socket portion, so that the rotational position of the centering disk relative to the flange portions of the flange yokes is not determined. Further, the rotational position as well as the radial position of the thin annular disks relative to the centering disk and the annular flange portions of the flange yokes are not determined either. Therefore, the centering disk and the thin annular disks are liable to suffer irregular and uneven wearing, thereby causing a substantial deterioration of the velocity constancy of the joint after a certain period of use. Further, since the socket portion is aligned to the diametrical center of the centering disk, when the joint is operated with a relatively large angle of intersection, or break angle, between the axes of the input and output rotary shafts, the peripheral portion of the centering disk is diametrically shifted relative to the annular flange portions of the flange yokes, or the annular groove in which it is slidably disposed, to such a great extent that, when the diameter of the centering disk is relatively large as compared with the diameter of the annular flange portions of the flange yokes, the break angle of the joint is limited to be relatively small by a peripheral edge portion of the centering disk abutting a bottom portion of the annular groove, while when the diameter of the central disk is relatively small as compared with the annular flange portions of the flange yokes, a peripheral portion of the centering disk is exposed so much out of the annular groove that the centering action of the centering disk is substantially lost.